1. Field of Invention
The invention relates to a light emitting module and, in particular, to a light emitting module having LEDs serving as light sources.
2. Related Art
A light emitting diode (LED) is a light emitting element made of semiconductor materials. When an extremely low voltage is applied across two electrode terminals of the LED, the redundant energy may be excited in the form of light according to the combination of electrons and holes.
Different from the typical incandescent light bulb, the LED pertains to the cold light emitting element and has the advantages of low power consumption, long lifetime, needlessness of the warm-up time and quick response speed. In addition, the LED has small size, can withstand vibration, is adapted to the mass production, and is adapted to the formation of the extremely small or array-type module according to the requirement of the application. Accordingly, the LED may be widely applied to indicators, advertising space and display devices of information, communication and consumer electronic products, and thus becomes the indispensable element in the daily life. Recently, the LED is further applied to a light source of the backlight module of a liquid crystal display (LCD) so as to gradually replace the conventional cold cathode fluorescent lamp (CCFL) to serve as the light source.
FIG. 1 is a schematic illustration showing a conventional side-edge backlight module 1. Referring to FIG. 1, the side-edge backlight module 1 includes a frame body 11, a plurality of LEDs 12, a circuit board 13, a light shield 14, a light guide plate 15 and a reflective sheet 16. The frame body 11 is a hollow rectangular frame body. The LEDs 12 are disposed on the circuit board 13, the circuit board 13 is vertically disposed in the light shield 14, and the light shield 14 is screwed to a lateral side of the frame body 11.
Referring to FIG. 2, the LED 12 has a chip 121, a lead frame 122 and a plastic housing 123. The chip 121 is disposed on the lead frame 122, and the plastic housing 123 covers one portion of the lead frame 122 with a lead L being exposed. The lead L of the LED 12 is adhered to the circuit board 13 by a conductive adhesive. The light outputted from the chip 121 is reflected to the plastic housing 123 by an inner wall of the plastic housing and a reflective layer on a surface of the lead frame 122.
The LEDs 12 are arranged in a row and disposed toward a light input surface 151 of the light guide plate 15. When the light rays outputted from the LEDs 12 enter the light guide plate 15 through the light input surface 151, the light rays are totally reflected inside the light guide plate 15 so as to achieve light mixing. When the light rays pass through printed dots on a bottom surface of the light guide plate 15, the light rays are scattered and the total reflection of the light rays is terminated. Thus, a portion of the light is refracted out of a light output surface 152 of the light guide plate 15, and then a plane light source can be formed.
However, when the side-edge backlight module 1 is being assembled, it is very difficult to align the LEDs 12 with the light input surface 151 of the light guide plate 15 because the sizes of the LEDs 12 are quite small and the height h of the light input surface 151 of the light guide plate 15 is also quite small. If the misalignment occurs, the light rays outputted from the LED 12 may not enter the light guide plate 15 so that the light emitting efficiency of the side-edge backlight module 1 is deteriorated. Furthermore, the light guide plate 15 is usually made of expensive resin, and the light guide plate 15 is formed by way of injection molding, so the cost of the side-edge backlight module 1 is also increased.
Furthermore, the light is mostly emitted from the bottom surface of the chip 121, and the reflective layer for reflecting the light is coated on the surface of the lead frame 122. Thus, most of the light can be emitted in a direction toward the top surface of the LED 12. However, the light availability is unavoidably decreased when the light is emitted out through the reflective layer so that the light emitting efficiency of the LED is decreased.
Therefore, it is an important subject to provide a light emitting module for solving the above-mentioned problems.